Printers such as inkjet printers which print onto a variety of print media such as paper or film are well known. As well as accepting print media in a single sheet format, some printers also accept print media fed from a supply roll of print media. Such a printer may be typically referred to as a roll-based printer, being a printer that accepts roll-based print media.
It will be appreciated that, in order to achieve consistent print quality, it is important that feeding of the print media is finely controlled. Variation in print media speed or tension may result in deterioration of print quality in the form of, for example, a distorted image.
Accurate control of print media feeding from a roll is particularly problematic in wide-format printing (otherwise known as large format printing), where the width of the print media is large, for example 32 cm to 150 cm (or even more).
The feeding of print media from a roll for a large format printer is typically undertaken by means of a roller that advances the print media with a traction provided by pinch wheels. The print media is pulled from a roll that has a mechanism to provide some tension (back-tension) to the media. A conventional approach to providing such tension is to use friction to produce a resistance to the rotation of the roll.
Controlling the tension in the print media is of high importance. If the tension is too high the print media can slip from the traction of the roller, and even a small slippage can produce undesirable printing artifacts and reduce print quality. Conversely, if the tension is too low, the print media may not be properly guided and/or controlled and the position of the media may deviate laterally. Further, wrinkles in the print media may be created due to a mismatch in traction at different parts of the roller.
Some roll-based printers also retrieve the print media in a roll after printing, by extracting the print media from the printer and collecting it on a spindle. For the same reasons as feeding of print media to a printer, controlling the media tension is also important in the case of retrieving print media from a printer.